1. Field of the Invention
The present invention relates to a rear wheel steering device for a vehicle which steers rear wheels in relation to a steering control for front wheels.
2. Description of the Prior Art
A conventional rear wheel steering device for a vehicle generally comprises: a rear wheel steering shaft extending in the widthwise direction of the vehicle body to be interconnected, at both ends thereof, with left and right rear wheels by means of tie rods respectively; an electric motor as a power source; and a transmission mechanism for transmitting an output from the electric motor to the rear wheel steering shaft. With this construction, the conventional rear wheel steering device for a vehicle steers the rear wheels, at low speeds, in the opposite phase to the front wheels to achieve higher turning performance, while, at high speeds, steers the rear wheels in the same phase as the front wheels to obtain higher running stability. One example of the conventional rear wheel steering device is disclosed in Japanese Patent Application Laying-open Gazettes No. 60-193771 and No. 62-25277.
To prevent failures, this type of a rear wheel steering device is provided with a clutch in the transmission mechanism and also centering spring means for pressing the rear wheel steering shaft to a neutral position. Accordingly, in case of failure, this clutch interrupts the transmission of the output from the electric motor to the rear wheel steering shaft through the transmission mechanism. At the same time, the centering spring means presses and holds the rear wheel steering shaft and the left and right rear wheels interconnected therewith in the neutral position.
However, when rotation of the electric motor exceeds the normal rotation range, in other words, in case of uncontrollable rotation of the electric motor, the rear wheels may be abnormally steered before the clutch is disengaged. The uncontrollable rotation of the electric motor is stopped when the rear wheel steering shaft is brought to interfere with other constituent members (for example, a supporting member for supporting the rear wheel steering shaft, etc.) and thus the axial displacement (displacement in the widthwise direction of the vehicle body) of the rear wheel steering shaft is restricted. However, this may cause a load to act on the clutch and may hinder the disengagement operation thereof.